/*
*    Qizx/open 3.0 beta
*
* This code is the open-source version of Qizx.
* Copyright (C) 2004-2009 Axyana Software -- All rights reserved.
*
* The contents of this file are subject to the Mozilla Public License 
*  Version 1.1 (the "License"); you may not use this file except in 
*  compliance with the License. You may obtain a copy of the License at
*  http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
*  WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
*  for the specific language governing rights and limitations under the
*  License.
*
* The Initial Developer of the Original Code is Xavier Franc - Axyana Software.
*
*/
using System;
using EvaluationException = System.Qizx.Api.EvaluationException;
using XQValue = System.Qizx.XQuery.XQValue;
using SingleSourceSequence = System.Qizx.XQuery.Dt.SingleSourceSequence;
namespace System.Qizx.XQuery.Fn
{
	
	public abstract class FilteredSequence:SingleSourceSequence
	{
		virtual public long Position
		{
			get
			{
				return position;
			}
			
		}
		virtual public long Last
		{
			get
			{
				if (last < 0)
				{
					XQValue sba = source.BornAgain();
					for (last = 0; sba.Next(); )
						++last;
				}
				return last;
			}
			
		}
		protected internal long position; // current position
		// caching last(): if last >= 0 , it is already evaluated
		protected internal long last = - 1;
		
		public FilteredSequence(XQValue source):base(source)
		{
		}
		
		public abstract override bool Next();
	}
}